1. Field of the Invention
The present invention relates generally to self-propelled, walk-behind traction vehicles, such as lawn mowers and various other turf maintenance equipment. More particularly, the present invention concerns an improved operator-manipulated drive control mechanism for controlling traction and steering of the vehicle.
2. Discussion of the Prior Art
Conventional self-propelled, walk-behind traction vehicles, such as lawn mowers, are increasingly including a pair of reversible, variable speed drive wheels so that the operator can control traction and steering of the vehicle. As those ordinarily skilled in the art will appreciate, dirigibility and reversibility is especially important with a large vehicle or with any vehicle used in an area having a large concentration of obstacles that must be avoided as the vehicle is maneuvered within the area. For example, with turf care equipment, it is desirable to have a machine with a relatively wide working width (e.g., cutting width) so as to reduce the time necessary to perform the desired maintenance on a given area of land. However, the increased size of the machine cannot cause it to become unwieldy, otherwise the operator will have difficulty in avoiding the trees, shrubs, fences and other obstacles encountered while moving across the ground.
In the past, the drive control mechanism has typically employed either a gear transmission or a hydrostatic transmission for selectively coupling the drive wheels to the engine. Gear transmissions are traditionally slow to respond to the operator's commands and are cumbersome when reversing directions or changing speeds. Obviously, such characteristics adversely affect the agility of the machine. Additionally, gear transmissions often do not allow the drive wheels to be driven in opposite directions, such that one drive wheel must be stopped while the other drive wheel is rotated to perform the highly desirable zero radius turn. It will be appreciated that the stopped wheel will often create "scuff" marks or otherwise damage the underlying ground. Although hydrostatic transmissions are traditionally more responsive than gear transmissions and more likely to afford independent control of the direction and speed of rotation of the drive wheels, hydrostatic transmissions are typically extremely expensive. Further, operation of a vehicle having a hydrostatic transmission tends to be "jerky" or abrupt; that is, the vehicle tends to lurch as it starts moving from a stopped position, reverses direction, or changes speed.
The maneuverability of the vehicle depends not only on the ability of the drive wheels to rotate in opposite directions and at various speeds, but also on the ability of the vehicle to respond quickly to the operator's commands and to immediately provide the operator with perceptible feedback of his/her commands so that necessary corrections or adjustments may be quickly determined and carried out. Accordingly, the operator-manipulated controls for controlling the transmission must operate in a manner that quickly and accurately converts the operator's commands to movement of the vehicle. The vehicle must also quickly convey to the operator the effect of those commands so that the operator can quickly respond, if necessary. Conventional drive controls are often tedious and difficult to manipulate and, more importantly, fail to place the operator and vehicle "in tune" with one another, such that the responsiveness of the vehicle to the operator's commands and the responsiveness of the operator to the effect of those commands are decreased. Of course, such reduction in responsiveness on the part of the vehicle and of the operator adversely affect the maneuverability of the vehicle.